1. Field of the Invention
The present invention relates to an optical component such as a lens. More specifically, the present invention relates to an optical component that has satisfactory low light-reflection, and a simple structure with a good outstanding strength, and in addition is excellent in terms of cost and productivity.
2. Description of the Related Art
Magnesium fluoride has been widely used as a material for a light reflection preventing film of various optical components such as a lens due to its inexpensiveness and low refractive index.
In an optical component, a reflection preventing film made of magnesium fluoride is generally formed on an optical component by vacuum deposition. However, an optical component itself absorbs moisture, so that the following is known: in order to obtain a reflection preventing film with sufficient strength as well as optical characteristics, excluding such an adverse effect, it is required to heat an optical component to high temperature (about 200° C. to 300° C.) during film formation (so-called “heating of a substrate”) so as to evaporate moisture.
As a material for an optical component, glass has conventionally been used. Glass has sufficient heat resistance against the above-mentioned high temperatures. Therefore, there is no problem in forming a magnesium fluoride film by conducting the above-mentioned high-temperature treatment.
On the other hand, recently, an optical component made of plastic has been used due to its light weight, low cost, and excellent productivity. However, as is well known, a plastic material for an optical component generally does not have sufficient heat resistance to the above-mentioned temperatures, so that it is impossible to form a film with such a high-temperature treatment. Furthermore, an attempt has been made to form a magnesium fluoride film by heating the material to a heat-resistant temperature of plastic (about 70° C. to 90° C.). Nonetheless, a product with sufficient characteristics (in particular, strength) has not yet been obtained.
In contrast, various methods have been proposed for forming a reflection preventing film made of magnesium fluoride with satisfactory mechanical strength on an optical component made of plastic without performing a high-temperature treatment. Examples of the film formation method include: ion-assisted deposition (IAD) in which a substrate is cleaned by irradiation with ions; an ion plating method intended for improving film quality by ionizing a substrate; vacuum deposition in a high vacuum state; vacuum deposition while irradiating a substrate with electron beams; vacuum deposition in which a vaporized film material is allowed to pass through a plasma region; a vacuum deposition by using cluster ion beams, and the like.
However, the above-mentioned methods have disadvantage in various aspects such as productivity, operability of film formation, and a cost.
Furthermore, there is a technique for forming a low reflection film with a multi-layer structure (multi-coat) in which films made of materials having various refractive indexes are combined. Similarly, such a technique has disadvantage in terms of productivity, a cost, and a yield.